A decrease in oxygen availability (hypoxia) can be encountered in solid tumors and has been associated with a poor outcome. Hypoxia can affect the function of many cells involved in tumor formation either directly or through the accumulation of adenosine. Both hypoxia and adenosine have been shown to inhibit the function of tumor infiltrating lymphocytes thus contributing to the failure of the immune system to fight cancer cells. The functionality of T lymphocytes relies on ion channels that control calcium (Ca2+) influx which is essential for the activation and function of these immune cells. Specifically two potassium channels, Kv1.3 and KCa3.1, play critical roles in the development and persistence of the Ca2+ response by regulating the driving force for Ca2+ influx. We have shown that hypoxia selectively inhibits the function and expression of Kv1.3 channels and decreases T cell proliferation and cytokine release. The mechanisms that mediate downregulation of Kv1.3 expression during hypoxia are not fully understood. Moreover, no information is available whether adenosine has any effect on these important channels and through them regulates T cell function. We have obtained preliminary evidence that adenosine inhibits the activity of KCa3.1 channels. Therefore, in the current application we will test the hypothesis that the microenvironment of solid tumors, and specifically hypoxia and adenosine, inhibit Kv1.3 and KCa3.1 channels producing a multidirectional attack on T cells that weakens the immune defense. We will perform experiments to identify the mechanisms that mediate downregulation of Kv1.3 expression in hypoxia. Furthermore, we will study the signaling pathways and functional relevance of KCa3.1 inhibition during hypoxia. We will also engineer multivalent nanoparticles to selectively target the expression of molecules involved in the decrease immune function by adenosine. Findings from the proposed studies will provide new insights into the mechanisms involved in decrease immune surveillance in solid tumors. Furthermore they will provide novel therapeutic targets and approaches to maintain the ability of immune cells to fight cancer cells in the hypoxic microenvironment.